The Dutch Republic

[Brutus]

Hmmm, well, most units fighting on the dutch side would have been mercenaries, mostly Germans and French. Some Walloons would be nice, as well for any Dutch army as for a Spanish army. These mercenaries would be mainly employed by prince William of Orange (who fled to Germany in 1567 and was murdered at Delft in 1584), his brothers and his sons and succesors.

More importantly though, you would have to include 'Geuzen' of 'Watergeuzen' (Seabeggars), which were groups of protestant Dutch that fled out of the Netherlands during the rule of the duke of Alva (1567-1573), who fiercely persecuted all protestants. The 'Watergeuzen' fled to sea and acted as pirates for some years before starting the real rise against Spain in 1572. The Watergeuzen are also known to have killed large numbers of Catholic clergy (most famous at Brill, were they killed 19 clergymen from Gorinchem). So they could be concieved as zealous protestants and pirates.

Many of the other units in the early war would have been city militia units, who would have quite well armed and trained, due to the rich cities in the region.

Last but not least, units from the Netherlands during the earlier periods should include 'Bandes d'ordonnance' or 'Ordonnantiebenden', which were units made up of young noble horsemen (heavy riders as well as 'archers') who were the only standing army in the Netherlands for quite some time. Charles the Bold (r. 1467-1477) first started these units, and after a brief interlude they re-emerged under Philip of Austria (around 1500). They remained in existance at least until the Revolt against Spain.

An other type of (in)famous unit would have been the 'Zwarte bende' ('Black gang'), who fought for the Duchy of Guelders (Gelre) against the Habsburgs (until 1543, when Charles V finally subdued Guelders). I don't know which kind of soldiers this gang was made of, though.

I will try to find some pictures of any Dutch soldiers of the period.